1. Field of the Invention
The present invention relates to a seat reclining apparatus for a vehicle, more particularly to a vehicle having a seat cushion and a seat back which is hinged to the seat cushion by a lower arm secured to the seat cushion and an upper arm secured to the seat back.
2. Description of the Prior Art
In Japanese Patent Laid-open Publication No. 59-34211, which corresponds to U.S. Pat. No. 4,523,786, there is disclosed a hinge device for seat-backs for adjusting the slope of the backs and locking them in their adjusted positions. The device has a pair of flanges fixed to the framework of the sitting portion of the seat (or, seat cushion) and the framework of the seat back, which are generally called as a lower arm and an upper arm, respectively, and the flanges are rotatably mounted on a shaft. Between the flanges, i.e. the lower arm and the upper arm, provided is a locking mechanism which has a toothed bolt (or, pawl) and an inwardly toothed sector (or, ratchet), and also provided is an unlocking mechanism which has a cam connected to a control hand-lever and adapted to coact with the bolt. In this prior device, the rotation of the upper arm relative to the lower arm is restrained, with the bolt (or, pawl) and the sector (or, ratchet) meshed with each other, while the rotation of the upper arm relative to the lower arm is allowed, with the engagement of the bolt (or, pawl) and the sector (or, ratchet) released from each other by manipulating the hand-lever.
According to the above-described prior device, however, when such load as to rotate the upper arm, in the condition, where the rotation of the upper arm relative to the lower arm has been restrained, is applied to the upper arm, its reaction force from the upper arm acts on the shaft. As a result, the hand-lever is loaded by the reaction force, and therefore the operability might be deteriorated.